This invention relates to a process for preparing a branched polymer from a vinyl aromatic monomer.
Free radical bulk polymerization is a well known process for preparing polymers from vinyl aromatic monomers. However, typical initiators used in these processes produce high viscosity, high molecular weight polymer in the early stages of polymerization, which can lead to gelling. Therefore, these processes are conducted at low temperatures, keeping the polymerization rate and viscosity low such that heat can be removed sufficiently and gelling is prevented.
Branched polymers have been produced from aromatic monomers in a variety of ways including the use of a vinyl functional initiator, such as n-butyl-t-butylperoxyfumarate, as described in U.S. Pat. No. 4,376,847. However, in this method, branching occurs in the polymerization reactor, causing gels to form. Gels build up in the polymerization reactor after extended periods of continuous operation and lead to reactor fouling.
Peritaconates have been used as chain transfer agents to retard the Mw growth in the production of polystyrene, polymethylmethacrylate and polybutylacrylate as described in WO 94/13705 by Nuhuis et al., of Akzo Nobel. Although it is mentioned that these chain transfer agents can also be used as polymerization initiators, the process in Nuhuis et al. produces polymers of low molecular weight, e.g. exemplified as having a Mn of between about 2,200 and 24,000.
Accordingly, it remains highly desirable to provide an efficient method of producing a branched polymer derived from a vinyl aromatic monomer which does not have the foregoing disadvantages of the prior art.